Process for firming cherries



ire rates Patent PROCESS FOR FG CHERRIES Dante G. Guadagni, Lafayette, Califi', assignor to United States of America as represented-by the Secretary of Agriculture No Drawing. Application March 18, 1957 Serial No. 646,938

3 Claims. (Cl. 99-193) (Granted under Title 35, U. S. Code (1952), sec. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughoutthe world, with thepower to grant sublicenses for such purposes is hereby granted tothe Governmer of theUnited States of America.

This application is a continuation in part of my copending application for patent Serial No. 449,281, filed Aug. 11, 1954, issued as PatentNo. 2,788,231.

This invention relates to and has among its objects the provision of methods for treating cherries for the purpose of increasing the quality of the fruit. A particular phase of the invention concerns procedures wherein cherries are subjected to a conditioning operation Whereby to increase the quality of the fruit, particularly to cause a firming of the fruit tissue. Additional objects of the invention will be evident from the following descrip- As well known in the industry, considerable quantities of red sour cherries are preserved by freezing. This product is commercially producedby packingthe-cherries, whole or pitted, in cartons together with about onequarter of their Weight of sucrose or an equivalent amount of syrup (sugar dissolved in water). The container is then closed and subjected to freezing. To prevent browning, ascorbic acid maybe addedto the sugar or syrup or the fruit may-bepre-treated with sulphur dioxide or other sulphiting agent suchas sodium'bisulphite. The resulting product is a Wholesome and nutritious food. However, in many cases the product after thawing is foundto be undesirably soft intcxturo Whenthe product is to be'used incooking, as in preparing pies or other bakery products, the additional softening effect of the cookingtreatmentrenders the fruit almost mushy.

it has now been found that-the problem of soft texture outlined above can be alleviated in a simple yet effective manner. This is done by first freezing-the cherriesand then subjecting them to What is termed a conditioning treatment. This treatment involves holding the cherries in thawed or unfrozen state, preferably at a 'tempera tu just above their freezing point from about /2 to about 6 days. During this conditioning treatment certain physical and/or chemical changes take place Whereby the fruit tissue becomes firm. After the conditioning treatment, the cherries may be consumed or otherwise utilized without further treatment. If the cherries are to be stored they are re-frozen and'maintained in frozen storage until ready to be consumed; During such refreezing and storage the cherries will retain the enhanced firmness developed during the conditioning treatment. Thus when the products are eventually thawed for consumption they will be found to be desirably firm in texture.

is to be noted that the firming effect'of the conditioning treatment is peculiar to cherries. it has not'been found to take place with any other fruits. it' is also to be emphasized that it is essential to freeze the cherries prior to the conditioning treatment. In the absence of prior freezing no increase in tissue firmness is obtained.

In'applying the process of the invention, the. cherries may be processed in their wholestate or they may be pitted or cut intopieces. Usually they are merely pitted before being subjectedto-the freezing and subsequent steps. In order to prevent browning, the cherries are preferably treated with a chemical agent, for example, sulphur-dioxide, sodium sulphite, sodium bisulphite, or ascorbic acid.

The cherriesmay be frozen-in any of the ways .as well known in the trade. For instance, they may be frozen in containers or on trays in tunnel or blast freezers.

The frozen cherries directly after freezing, of after storagea-t freezing temperatures, are subjected to the conditioning treatment.- This' is accomplished'by simply placingthe frozen cherries in a zone maintained at a temperature just above the freezing point of the cherries, such conditions being-maintained for a period of time sufficient to allow the tissue firming to take place. The frozen cherries will, of course, thaw when subjected to these conditions. If desired, the frozen cherries may be deliberately thawed by other means and then directly Without any delay subjected to the conditioning treatment. The conditioning temperature to be used with any particular batch of cherries willdepend on the composition of the cherries; particularly their solids content. Thus fruit with a low solids content will have a relatively higher freezing temperature than fruit of higher solids content. In general theconditioning temperature may be from about 25 F. to about 35 F. and it is preferred to employ a temperature Within this range which is just above the freezing point of the cherries, thatis, about 0.5 to 5 F. above the freezing point. Under such conditions the treatment will operate satisfactorily and there will be no-danger of microbial spoilage during the conditioning treatment. The firming of the cherry tissue does not occur rapidly-and sufficient time must be allowed for the firmness to develop. This time will vary depending on the maturity andcomposition of the cherries and maytake-from /z day, preferably 1 day to about 6 days. In any particular case the time necessary for proper'firmness development can be easily determined'by checking the texture of the cherries with suitable instruments and discontinuing the conditioning when thedesired degree offirmness is established.

After the conditioning operation is completed, the cherries may be treated in various ways. Thus for example the conditioned cherries may be frozen and maintained in frozen storage, in the alternative, the conditioned cherries may be subjected to dehydration to reduce their moisture content to a low level so that the product will be self-preserving. The conditioned cherries may also be-preserved by canning. Other preservative methods such asbrining, candying, etc. may be applied to the conditionedcherries. If the conditioned cherries are not to be preserved they may be consumed directly or used in the preparation of pics, tarts, cakes or the lik EXAMPLE I A lot of: fresh, pitted, red sour cherries having their natural moisture content and containing no added material was frozen by subjection to an air blast atrniuus 20 F. The frozen cherries weredivided into four sampies. One sample was stored in a freezer at minus 10 F. for 5 days; the other three. sampleswere stored in a These firmness tests were "l'enderometeri and measuring the force required for the blades to cut through the fruit. are tabulated below: i a

It is evident from the above'data that the'previously if frozen cherries which were maintained at-34. F; for

days showed a greatly increased tissue firmnesswhereas the product stored in the frozen state at minus F.

(sample b) did'not increasein firmness,

In'the process as illustrated in Example I, the cherries were subjected to the conditioning'withoutadding any material whatever so that it is evident that the, increase in firmness is attributable solely to the efiect of the conditioning treatment- The results obtained 7 ditioning treatment described aboye.

tioning operation, the product may be consumed or other' wise utilized without further treatment. If the product 1 is to be stored it may be re-frozen or preserved in other a in the usualway. After the product has .been frozen it;

is removed from the freezer and subjected'to' the con- After the condiways as by dehydration, canning,;brining, etc.

When carrying out the conditioning in this .manner,

thesfruit is in contact with thesyrup'snrrounding it and z 1 sugarwill diffuse from the syrup into the fruit tissue.

This conditioning is'so effective that the sugar content of the fruitfwillbecome equal to the sugar content of the syrup." Thus originally the'fruit has a lower sugar concentration than thelsurrounding syrup. As the condimming proceedsisugal" fi S 'into'the fruit tissues with the result that the sugar content of the firuitin creases whereas the sugar content of the syrup decreases.

It is within the purview of this invention toutilize the conditioning treatment to 'efiect other quality improve+- ments in'addition to causing a -firrn ing of the cherry tissue. Thus the conditioning treatment-may be'used to impregnate the cherry tissue with sugar (or other food ingredient) simultaneously with eifectuating the tissue firming. To this end, the cherries during the conditioning are maintained in contact with a solution or dispersion of a food ingredient, for example, sugar. It is to be noted that cherries are the only fruit which we have found to undergo increase of firmness when subjected to this impregnation treatment. This aspectof the invention is further. explained as follows d When cherries packed with sugar or sugar syrup are cherries themselves are quite tart. Further, their tartness 1S psychologically intensified to the consumers palate when the product is eaten because of the sharp contrast 'between the tartness of the fruitand the sweetness of the surrounding syrup. The industry has long soughtfor toobviate this contrast in taste between fruit and syrup. Thus various'techniqueshave been advocated to accomplish such an end. For example, one recommendedpi'ocedure 1S toapply dry sugar or syrup to the cherries and 7 then permit the mixture to stand for some time prior to freezing' Such a technique will cause some of the sugar to enter the fruit tissue but the rateof internal sweetening'which occurs is very slow and usually such standing fora day or two will increase the sugar content of the fruit by about 5% at the maximum. Another technique known in the art involves subjecting amiX- ture of the fruit and syrup to a' vacuum'followed by release of the vacuum whereby to cause syrup to be drawn into the fruit tissue. This technique gives a greaterin-' crease in internal sugar content butis truly effective only with fruits like apples and pears, the tissue of which normally contains a substantial proportion of air whereto thesarne'level asjthe sugar content of the syrup. As

Finally an equilibrium point is reached at which thesugar contents ofthe tissue and syrup are equal. Siich'aresult,

that is, such an exhaustive absorption of. sugar by the fruit cannot be obtained by the previously known method, 2 ;that is where the untreated fruit is simply allowed to stand in contact with isugar or syrup prior to freezing. Thus my researches have shown that the freezing must take place prior to the conditioning operation to obtain 7 q a high degree of sugar. absorptioninto the fruit tissues in a practical period of time. It is also to be noted that the a frozen in conventional manner, it is found that-the" a method by which cherries could be internally sweetened desirable in that they not only add their sweetening effect. but also the characteristic fruity'taste so that the flavor f by the space formerly occupied by air can be filled with the syrup, However, even with vacuum impregnation it is impossible to bringthe sugar content of the fruit up a a result'tartfruit impregnated with syrup will still exhibit a strong taste contrast'as compared with the syrup surrounding it.

.The problem outlined above'ean be readily alleviated by application ofthe process of this invention, namely, by conditioning the fruit Whilejinqcontact with a sugar solution. "As an example .of [the procedure, frozen cherries are prepared in the conventional manner, that is, thefruit is packed into a container together with dry sugar or sugar syrup. The sugaredfruit is. then frozen absorption of sugar is accompanied by firming of the fruit tissue as previously explained. V j Although the above discussion is concerned with the absoiption of sugar into thefruit tissue, the invention also encompasses the conditioningof cherriesrunder. such circumstances as'to causethe fruit to absorb any desired solu ble ingredient with simultaneous firming of the. cherry 7 tissue. Thus instead of sugar, the substance may .be'a

flavoring agent, a nutritive agent, a coloring material, a preserving agent, a flavor-intensifying agent or any com:

bination of these. The nature of the substance is im-? material as'the same effect will take place. Examples of food ingredients which maybe incorporated in water or other edible liquid to formthe impregnating liquid are.

set forth below:

Sweetening agentszi sucrose, dextrose, fructose, maltose,

invert sugaiycorn syrup, molasses, maple sugar or syrup,

'etc. Forthe so-called dietetic foods, saccharin or sodium cyclamate may beused. Particularly desirable sweetening agents are the concentrated fruit juices and especially full-flavored concentrates, that is, those in which the volatile essences usually, lost in evaporative techniques are recovered by condensation 'or other'means and returned to the concentrate. Fruit juice concentratesfare of the treated fruit is intensified. 'Novel effects may be obtained by using a full flavored fruit juice derived from a diflierent fruit to impregnate the cherries.

, Other flavoring agents: salt, citricacid, alcoholic 'extracts such as vanilla, lemon, mint,etc., soluble extractives from fruits or vegetables, wines, synthetic flavorings, such as vanillin and methyl anthranilate, natural fruit essenses suchas, those'recovered by condensation or other technique from the .vapors evolved in the evaporation of truit juices, etc.. 7 V 7 a d V Nutritive" substances: vitamins, vitamin precursors, mineral salts, proteins, solubilized starch, amino acids, sugars, etc.

mColoring materialsz dyes suitable for food use, juices-' from highly pigmented fruits oi' vegetables, for instance,

Concord v grape juice, extractives from pigmented edible;-

plant materials, etc. V,

Preserving agents: browning inhibitors such as sodium sulphite, sodiuin'bisulphite, ascorbic acid, lemon. juice, 7

etc. Fat-stabilizing agentslsuch' as nordihydro'g uaia'retic acid, propyl gallate, tertiary-butylated :hydroxyanisolc.

. ethyl hydrocaifeate, etc. Agents for preventingor. inhibitingmicrobialspoilage such as sodium benzoate, sodium parahydroxybenzoate, ethyl vanillate, antibiotics, etc.

To promote the diffusion of the'food ingredients into the cherries during the conditioning operation, the concentration of the food ingredient in the edible liquid should be greater than the concentration of the same ingredient in the cherries. For example, if the cherries to be treated contain sugar the concentration of sugar in the edible liquid should be higher than thus to provide a driving potential for the diffusion process.

In applying the process of the invention to cherries in order to sweeten them and firm their tissue, a preferred procedure involves conditioning the cherries while they are in intimate contact with an aqueous solution containing at least 20% sugar, the conditioning being continued until the fruit and the solution each contain essentially the same concentration of sugar, within the range about from 20 to whereby the fruit and the liquid have substantially the same degree of sweetness. The resulting mixture of fruit and liquid is then preferably frozen and maintained in frozen condition until they are to be consumed.

When conducting the conditioning of cherries in the presence of a liquid preparation of a food ingredient in order to accomplish both firming of the cherries and an impregnation of the cherry tissue with the food ingredient, sufiicient time must be allowed for the impregnation to take place. Obviously, the time for penetration of the food ingredient into the tissue will depend on such factors as the degree of impregnation desired, the nature of the cherries, that is, their porosity or denseness, the size of the cherries or pieces thereof, the relative concentration of the food ingredient in the surrounding liquid as compared with the concentration thereof in the cherry tissue, etc. To secure maximum penetration the conditioning is usually continued for a period from about /2 day, preferably one day, to about 6 days. The conditioning temperature is as described above, that is, the cherries are maintained in contact with the liquid containing the food ingredient at a temperature just above the freezing point of the cherries, within the range from about 25 to about F. Although the conditioning temperature is high enough to keep the cherries in a thawed condition so that impregnation with the food ingredient and firming of the tissue take place at a practical rate, the temperature is not so high as to cause damage to the color, flavor, nutritive value, or sanitary condition of the fruit.

After the conditioning operation is completed, the cherries may be treated in several ways. Thus for instance the impregnated fruit with the accompanying edible liquid may be frozen and maintained in frozen storage. If desired, the fruit may be separated from residual edible liquid and the fruit frozen and maintained in frozen storage until ready for consumption. In the alternative, the separated fruit may be preserved by dehydration. The impregnated cherries with or without the residual edible liquid may be preserved by other conventional techniques such as canning, brining, candyiug, and the like. If the impregnated fruit is not to be preserved it may be consumed directly or used in preparation of bakery products, desserts, etc.

As noted above, a preferred technique involves a procedure wherein cherries enveloped with an edible liquid containing a food ingredient are frozen then subjected to the conditioning operation. In an alternative plan, the cherries per so are frozen then subjected to the conditioning step while maintained in contact with the edible liquid. As an example, sour cherries are washed, pitted and frozen. The frozen cherries are then placed in a vessel and mixed with sucrose solution. The resulting mixture is then subjected to the conditioning operation to cause the cherries to become firm and to cause the sugar to penetrate into the fruit tissue.

Red sour pitted cherries were placed in cans together with enough 60 Brix'sucrose syrup to cover the fruit. The cans were sealed and frozen at'minus 10 F. The cans of cherries were then placed in a refrigerator maintained at 34' F., samples being withdrawn from'time to time and tested for firmness and sugar content. The firmness tests were performed by placing drained cherries in a conventional Tenderometer and measuring the force required for the blades of the instrument to cut through the cherries. The cherries were at room temperature in conducting these tests. The results obtained are tabulated below:

Efiect of storage at 34 F. on previously frozen sugared ch errzes Time of Firmness Sugar con- Sample storage at of cherries, tent of 34 F., days lbs. per cherries, sq. in. percent zero 41 20. 4 1 46 25. 6 2 54 26 3 26 6 60 28 All of the above products were tasted. It was observed that sample a (not conditioned) was tart whereas samples 52, c, d, and e were sweet. It was also observed that all the conditioned samples of cherries had good eating texture and the degree of firmness attained even by the product stored for 6 days was not so advanced as to be considered chewy.

EXAMPLE III Red sour cherries were washed and pitted then placed in cans. The fruit in the cans was covered with a 60 Brix solution of sucrose in water. The cans were sealed then frozen at minus 10 F. The cans of frozen product were then placed in a refrigerator maintained at 30 F. and samples were withdrawn and tested for sugar content in the fruit and surrounding syrup. In these tests the fruit and syrup were separated by draining through a sieve. The soluble solids content (largely sucrose) in the fruit and the syrup was then determined by the use of a refractometer. The following results were obtained:

Soluble solids content, Period of expressed as percent of Product storage at sucrose 30 F., days Fruit Syrup In addition to the above tests, the products conditioned at 30 F. (B and C) and the product which had not been conditioned (A) were tasted. It was found that products B and C were sweet and there was essentially no dif ference in sweetness between the fruit and the syrup. In the case of product A, the fruit was very tart whereas the syrup was very sweet. it was also noted that products B and C were firmer in texture than product A.

Having thus described my invention, I claim:

1. A process for improving the textural qualities of cherries which comprises freezing fresh cherries, then directly subjecting the cherries to a conditioning treatment wherein they are maintained in a thawed condition at a temperature just above their freezing temperature, within the range from about 25 F. to about 35 F., from about /2 to about 6 days, whereby to cause firming of the cherry tissue.

sour cherries having their'natural moisture contenfc. 2,788,281

7 V ReEe'rences'Cited in -the file of this patent UNITED STATES PATENTS V 1,480,607 'Ford Jan. 15, 1924' Zarotschenzeff Dec. 28,: 1937 Birdseye l Aprg 29,1941 Noyes June 22,1948 Guadag11i' :APLTQQ 19 57 if v 

1. A PROCESS FOR IMPROVING THE TEXTURAL QUALITIES OF CHERRIES WHICH COMPRISES FREEZING FRESH CHERRIES, THEN DIRECTLY SUBJECTING THE CHERRIES TO A CONDITIONING TREATMENT WHEREIN THEY ARE MAINTAINED IN A THAWED CONDITION AT A TEMPERATURE JUST ABOVE THEIR FREEZING TEMPERATURE, WITHIN THE RANGE FROM ABOUT 25*F. TO ABOUT 35*F., FROM ABOUT 1/2 TO ABOUT 6 DAYS, WHEREBY TO CAUSE FIRMING OF THE CHERRY TISSUE. 